A copying machine with an automatic original reading device reads both sides of original sheets even when original sheets printed on both sides and original sheets printed on one side are mixed.
However, in this method, blank sheet side of the original sheet printed on one side is also read. As a result, the process speed is decreased because of unnecessary data processing.
In addition, when printing out of the read original is performed, a blank sheet side without printing information is also printed, which results in a waste of paper resource.
To solve those problems, Japanese Patent Application Laid-Open No. 2004-147193 proposes a blank sheet determination method in which a compression process is performed on image data obtained from a read original, and the data quantity of the compressed data is used for determining whether or not the read original is a blank sheet.
In addition, Japanese Patent Application Laid-Open No. 2009-021681 proposes a blank sheet determination method in which an edge portion of image data obtained from a read original is detected, and the detected edge quantity is used for determining whether or not the read original is a blank sheet.